//  BinaryTournament.java
//
//  Author:
//       Antonio J. Nebro <antonio@lcc.uma.es>
//       Juan J. Durillo <durillo@lcc.uma.es>
//
//  Copyright (c) 2011 Antonio J. Nebro, Juan J. Durillo
//
//  This program is free software: you can redistribute it and/or modify
//  it under the terms of the GNU Lesser General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  (at your option) any later version.
//
//  This program is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU Lesser General Public License for more details.
// 
//  You should have received a copy of the GNU Lesser General Public License
//  along with this program.  If not, see <http://www.gnu.org/licenses/>.

package etmo.operators.selection;

import etmo.core.Solution;
import etmo.core.SolutionSet;
import etmo.util.PseudoRandom;
import etmo.util.comparators.DominanceComparator;

import java.util.Comparator;
import java.util.HashMap;

/**
 * This class implements an binary tournament selection operator
 */
public class BinaryTournament extends Selection {

	/**
	 * Stores the <code>Comparator</code> used to compare two solutions
	 */
	private Comparator comparator_;

	/**
	 * Constructor Creates a new Binary tournament operator using a
	 * BinaryTournamentComparator
	 */
	public BinaryTournament(HashMap<String, Object> parameters) {
		super(parameters);
		if ((parameters != null) && (parameters.get("comparator") != null))
			comparator_ = (Comparator) parameters.get("comparator");
		else
			// comparator_ = new BinaryTournamentComparator();
			comparator_ = new DominanceComparator();
	} // BinaryTournament

	/**
	 * Performs the operation
	 * 
	 * @param object
	 *            Object representing a SolutionSet
	 * @return the selected solution
	 */
	public Object execute(Object object) {
		SolutionSet solutionSet = (SolutionSet) object;
		Solution solution1, solution2;
		solution1 = solutionSet.get(PseudoRandom.randInt(0, solutionSet.size() - 1));
		solution2 = solutionSet.get(PseudoRandom.randInt(0, solutionSet.size() - 1));

		if (solutionSet.size() >= 2) {
			while (solution1 == solution2) {
				solution2 = solutionSet.get(PseudoRandom.randInt(0, solutionSet.size() - 1));
			}
		}
		int flag = comparator_.compare(solution1, solution2);
		if (flag == -1)
			return solution1;
		else if (flag == 1)
			return solution2;
		else if (PseudoRandom.randDouble() < 0.5)
			return solution1;
		else
			return solution2;
	} // execute
} // BinaryTournament
